Image indexing systems

ABSTRACT

An image indexing system comprising a video frame store, an averager which provides a first signal indicative of the average brightness level of each frame stored, an image splitter and averager which divides each frame into contiguous blocks of pixels, and provides for each block, a second signal indicative of its average brightness level, a comparator which compares each of the second signals with the first signal so as to produce in respect of each block a binary signal indicative of whether or not its brightness level, as indicated by the first signal, is greater or less than the average brightness level for the frame as indicated by the first signal, thereby to produce for each frame, an index signal comprising one binary bit for each block which serves to identify each frame for indexing purposes.

This invention relates to image indexing systems and more especially itrelates to systems for the indexing of video images.

There is a requirement for tagging each frame, or group of frames of avideo clip for example, with a characteristic index number so that amass of video material can be rapidly searched in order to identify aparticular frame or group of frames having the same index number.

It is readily apparent that such an indexing system may find a widevariety of applications wherein automatic searching through videomaterial is required in order to find a particular image or indeed inorder to establish whether a particular image is present in the materialsearched.

It is an object of this invention to provide a video imageidentification system which is comparatively simple and inexpensive toproduce, wherein image identification is effected with a high degree ofconfidence.

According to the present invention, an image indexing system comprises avideo frame store, an averager which provides a first signal indicativeof the average brightness level of each frame stored, an image splitterand averager which divides each frame into contiguous blocks of pixels,and provides for each block, a second signal indicative of its averagebrightness level, a comparator which compares each of the second signalswith the first signal so as to produce in respect of each block a binarysignal indicative of whether or not its brightness level, as indicatedby the first signal, is greater or less than the average brightnesslevel for the frame as indicated by the first signal, thereby to producefor each frame, an index signal comprising one binary bit for each blockwhich serves to identify each frame for indexing purposes.

In the case of colour images, data representative of the image may firstbe converted to monochrome using RGB averaging in order to providemonochrome data for the frame store.

The overall average brightness level may be computed for each frame byaveraging the brightness level of all pixels which comprise the frame.

The imager splitter may operate to divide each fame into rows andcolumns of contiguous rectangular pixel blocks.

The indexing system may form a part of image identification apparatuswhich additionally comprises a database in which the binary index foreach of a plurality of images is stored and a further comparator whereina binary index of an image to be identified as established by the imageindexing system, is compared with the indices stored thereby to providean output signal if the index of the image to be identified correspondsto the index of a stored image, the output signal including data whichidentifies the stored image in respect of which correspondence obtains.

The output signal my also include confidence level data derived independence upon the degree of correspondence which obtains between theindex of an image to be identified and the indices of stored images.

The system may include a confidence level threshold detector wherebyimages may be selected from the store if a predetermined percentagematch obtains between the index of a stored image and the index of animage to be identified.

It may be arranged that the threshold for selection is arranged to bevariable so that it can be set to correspond to a predeterminedpercentage match.

One embodiment of the invention will now be described by way of exampleonly with reference to the accompanying drawings in which:

FIG. 1, is a generally schematic block diagram of an image indexingsystem;

FIG. 2, is a generally schematic block diagram of image identificationapparatus which embodies the system of FIG. 1, wherein correspondingparts bear the same numerical designations;

FIG. 3, is one example of an image to be indexed;

FIG. 4, shows a multi block representation of the image of FIG. 3; and

FIG. 5, is a block representation of index signals corresponding toFIGS. 3 and 4.

Referring now to FIG. 1, an image indexing system comprises a videostore 1, for monochrome data corresponding to an image frame, which isfed thereto via an input line 2. The pixels which comprise each frameare sampled in a frame averager 3, thereby to produce a signal on a line4, which corresponds to the average brightness level B, of each frame.The image data from the video store is also fed to an image splitter 5,which serves to divide the image into a number of contiguous rows andcolumns of pixel blocks 6, as shown in FIG. 4, the grey scale brightnesslevel of each of the blocks 6, being determined by a block averager 7,which provides in respect of each block, a brightness level signal K, ona line 8, thereby to produce for the whole frame a grey scale imagecomprising blocks 6, as shown in FIG. 4.

The signals B and K on the lines 4 and 8 respectively, are fed to ablock comparator unit 9, wherein a binary ‘1’ or ‘0’ decision is made inrespect of each block which indicates whether it's brightness K, isgreater or less than the brightness average B, of the frame, whereby anoutput signal is produced on a line 10, from the comparator unit 9,which comprises a series of ‘1’s and ‘0’s corresponding to a binaryindex signal characteristic of the frame, which index signal isrepresented graphically as shown clearly in FIG. 5.

The index signal on the line 10, is fed to a database 11, wherein it isstored along with other identifying data provided on lines 12 and 13,which serve to classify video material identity and time coderespectively.

As shown in FIG. 2, the systems shown in FIG. 1, may be used in imageidentification apparatus, in order to provide for searching of an indexdatabase to identify a particular frame or frames. Referring now to FIG.2, the apparatus comprises, in addition to the system of FIG. 1, afurther comparator 14, and a database 15, which may correspondsubstantially to the database 11, shown in FIG. 1. In operation of theapparatus the index of an image to be identified is fed to the furthercomparator 14, wherein it is compared with the indices of images storedin the database 15. An output signal from the further comparator 14, isarranged to be delivered on an output line 16, if full correspondenceobtains between the index of the image to be identified and one of theindices stored in the database 15, the signal on the line 16, beingarranged to include data which serves to identify which of the storedindices is selected. Although not shown in the drawing it is envisagedthat in some circumstances a threshold detector may be provided which issettable to a level corresponding to predetermined percentagecorrespondence between the index of an image to be identified and theimage as represented by indices stored.

It will be appreciated that in operation of the system as hereinbeforedescribed, data appertaining to an image and produced on the line 10, isstored in the database bit by bit and when used in the apparatus asshown in FIG. 2, a score value as indicated by correspondence between animage to be identified and a stored image is progressively incremented,a potential match being indicated in dependence upon the score value.Thus a perfect score is deemed to be a perfect match and partial matchesare scored accordingly.

It will be appreciated that accurate results may be obtainedirrespective of colour brightness or resolution even when thesecharacteristics tend to differ slightly from that of an ideal image.

It will further be appreciated that various modifications may be made tothe arrangements hereinbefore described without departing from the scopeof the invention and for example the databases 11 and 15, and or thestores maybe arranged to form a part of a commercially availablecomputer/PC.

1. An image indexing system comprising a video frame store, an averagerwhich provides a first signal indicative of the average brightness levelof each frame stored, an image splitter and averager which divides eachframe into contiguous blocks of pixels, and provides for each block, asecond signal indicative of its average brightness level, a comparatorwhich compares each of the second signals with the first signal so as toproduce in respect of each block a binary signal indicative of whetheror not its brightness level, as indicated by the second signal, isgreater or less than the average brightness level for the frame asindicated by the first signal, thereby to produce for each frame, anindex signal comprising one binary bit for each block which serves toidentify each frame for indexing purposes.
 2. An image indexing systemas claimed in claim 1, wherein data representative of an image isconverted to monochrome using RGB averaging in order to providemonochrome data for the frame store.
 3. An image indexing system asclaimed in claim 2, wherein the overall average brightness level iscomputed for each frame by averaging the brightness level of all pixelswhich comprise the frame.
 4. An image indexing system as claimed inclaim 2, wherein the imager splitter operates to divide each frame intorows and columns of contiguous rectangular pixel blocks.
 5. An imageindexing system as claimed in claim 2 which forms a part of imageidentification apparatus and which additionally comprises a database inwhich the binary index for each of a plurality of images is stored and afurther comparator wherein an index of an image to be identified asestablished by the image indexing system, is compared with indicesstored in the database, thereby to provide an output signal when theindex of the image to be identified corresponds to the index of a storedimage, the output signal including data which identifies the storedimage in respect of which correspondence obtains.
 6. An image indexingsystem as claimed in claim 1, wherein the overall average brightnesslevel is computed for each frame by averaging the brightness level ofall pixels which comprise the frame.
 7. An image indexing system asclaimed in claim 6, wherein the imager splitter operates to divide eachframe into rows and columns of contiguous rectangular pixel blocks. 8.An image indexing system as claimed in claim 6 which forms a part ofimage identification apparatus and which additionally comprises adatabase in which the binary index for each of a plurality of images isstored and a further comparator wherein an index of an image to beidentified as established by the image indexing system, is compared withindices stored in the database, thereby to provide an output signal whenthe index of the image to be identified corresponds to the index of astored image, the output signal including data which identifies thestored image in respect of which correspondence obtains.
 9. An imageindexing system as claimed in claim 1, wherein the imager splitteroperates to divide each frame into rows and columns of contiguousrectangular pixel blocks.
 10. An image indexing system as claimed inclaim 9 which forms a part of image identification apparatus and whichadditionally comprises a database in which the binary index for each ofa plurality of images is stored and a further comparator wherein anindex of an image to be identified as established by the image indexingsystem, is compared with indices stored in the database, thereby toprovide an output signal when the index of the image to be identifiedcorresponds to the index of a stored image, the output signal includingdata which identifies the stored image in respect of whichcorrespondence obtains.
 11. An image indexing system as claimed in claim1 which forms a part of image identification apparatus and whichadditionally comprises a database in which the binary index for each ofa plurality of images is stored and a further comparator wherein anindex of an image to be identified as established by the image indexingsystem, is compared with indices stored in the database, thereby toprovide an output signal when the index of the image to be identifiedcorresponds to the index of a stored image, the output signal includingdata which identifies the stored image in respect of whichcorrespondence obtains.
 12. An image indexing system as claimed in claim11, wherein the output signal includes confidence level data derived independence upon the degree of correspondence which obtains between theindex of an image to be identified and the indices of corresponding tostored images.
 13. An image indexing system as claimed in claim 12,wherein the system includes a confidence level threshold detectorwhereby stored images are identified if a predetermined percentage matchobtains between the index of a stored image and the index of an image tobe identified.
 14. An image indexing system as claimed in claim 11,wherein the system includes a confidence level threshold detectorwhereby stored images are identified if a predetermined percentage matchobtains between the index of a stored image and the index of an image tobe identified.